1. Field of the Invention
The present invention relates to bags for storing items and, more particularly, to multisubstrate vertical form, fill, and seal (VFFS) bags that are simultaneously formed and filled. The invention additionally relates to a machine and a method for forming and filling such bags.
2. Discussion of the Related Art
In order to prevent the premature spoilage of produce and other perishable items, bags storing such items often are formed at least in part of an open mesh material. The open mesh ventilates the items in the bag or allows them to “breathe,” increasing the items' shelf life. The use of open mesh material in bags offers the additional advantage of rendering the stored items highly visible to potential purchasers.
The mesh material can be preformed into the shape of a bag and filled and different times and/or locations using separate forming and filling equipment. Alternatively, the bags can be formed, filled with items, and sealed simultaneously. One such type of bag is a “vertical form, fill, and seal” or “VFFS” bag that is formed and filled while a web is pulled downwardly over a hollow forming tube, then sealed from below, then filled with items, and then sealed from above. VFFS bags however, historically were formed entirely of film.
More recently, so called “half-and half” or other multisubstrate VFFS bags were introduced that are formed from a web that is part open mesh fabric and part film. Multisubstrate VFFS bags typically are generally square in shape and have both the front and rear walls formed from a strip of a film material that can be printed with indicia providing information about the items stored in the bags. These strips thus often are called “print bands.” In addition to bearing indicia, the strips also add dimensional stability to the bag, permitting the bag to stand more upright. This added dimensional stability enhances the bags' aesthetic appearance and permits more bags to be placed in a given area such as on a store shelf.
Bags usually are positioned at their point of purchase with the print bands facing outward. Because these bags are generally square in shape, the items in the bags are not easily viewed by potential purchasers, particularly if they are placed closely adjacent to one another on a shelf. This reduced visibility negates or at least mitigates the “viewability” benefits of making bags from an open mesh material in the first place.
The viewability of items stored in a VFFS bag could be improved by reducing the width of the film strips at the front and rear walls of the bag. However, since the film strips typically contribute the majority of the dimensional stability to a bag, VFFS bags with narrow print bands tend to be dimensionally unstable and, thus, “slouch” rather dramatically. This slouching reduces the aesthetics of the bags and also hinders the orderly placement of bags on shelves next to one another. It also reduces the number of bags that can be placed in a given area, a major concern in grocery stores and other applications where shelf space is at a premium.
The percentage of open mesh in a bag of a given capacity, and thus its viewability, can be increased by gusseting the mesh side walls of the bag. However, the typical gusseted bag produces a “bunched” structure at the bottom of the bag that prevents the bottom of the bag from lying flat and, thus, reduces the dimensional stability of the filled bag, counteracting one of the benefits sought by adding film strips to the bag.
The need therefore has arisen to provide a partial mesh VFFS bag that is dimensionally stable, aesthetically pleasing, and enhances the viewability of items stored in the bag.
The need also has arisen to provide a method and system for producing VFFS bags having the characteristics described above.